Rotary impact drill



March 2, 1965 w. E. STEWART 3,171,286

ROTARY IMPACT DRILL.

Filed Dec. 2G, 1962 2 Sheets-Sheet 1 bf :f1-gl D 44 INVENTOR.4 4% 44a Wam? E. fw/qnr March 2, 1965 w. E. STEWART ROTARY IMPACT DRILL 2 Sheets-Sheet 2 Filed Dec. 20, 1962 7W um? mg United States Patent O 3,171,286 ROTARY IMPACT DRHJL Walter E. Stewart, Shaker Heights, Ghia, assigner t Rubbermaid Incorporated, Wooster, (Ehio, a corporation of Ohio Y Fiied Dec. 2t), 1962, Ser. No. 246,234 1() Claims. (l. '74-22) This invention relates to improvements in a rotary impact tool having a shaft adapted to be connected at one end to a drive means and to carry a rotating tool such as a drill at the other end and having an impact selector movable between two positions, in one of which it permits rotation of the drill in the usual manner of a rotary drill, and in the other selector position causing repeated impacts of a hammer member against an anvil member connected with the drill While at the same time the drill is being rotated.

One ofthe objects of the present invention is to provide an improved rotary impact drill as described above wherein all of the working parts other than the impact selector and the drive means may be assm'bled and adjusted outside of the associated housing, and thereafter inserted in the housing as a unit.

Another object of the present invention is to provide novel means for adjustment of the tension of the spring which delivers the impact to the rotating tool.

Another object of the present invention is to provide for the accurate adjustment of the relative position between an impact causing cam and its follower, together with positive means for holding such adjustment.

Another object of the present invention -is to provide a tool of the type described with the minimum transmission of impact to the drive means or to the hand of the operator holding the rotary impact tool.

Another object of this invention is to provide a reduction of the inertia load on the drive means during the impact operation of the tool.

Another advantage of the present invention is that it provides an improved substantially frictionless movement of the impact receiving anvil in the associated housing during impact operation of the tool.

A further object ofthe invention is to provide improved mounting of the hammer on the drive shaft for positive drive by the shaft and for substantially frictionless reciprocation relative to the shaft. Y

A further object of the present invention is to provide novel and quickly adjustable means for varying the tension of the impact causing spring or for quickly mounting springs of different strength in the appropriate location in the tool.

Still another object of the invention 4is to provide a novel impact controller and means for holding it either in or out of impact-causing position.

Other objects and advantages of the present invention will be apparent in thel accompanying drawings and description vandthe essential features thereof will be set forth in the appended claims.

In the vdrawings-V FIG. 1 is a side elevational view of my improved tool incorporated in a hand held device;

FIG. 2 is a top plan view of the tool shown in FIG. l;

FIG. 3 is a central sectional view of the device of FIGS. l and 2, enlarged, and taken generally along the FIG. 4is a fragmental sectional view taken at approximately the center of FIG. 3 and showing the impact-causing cam and its associated follower in a position different from that of FIG. 3;

3,171,286 Patented Mar. 2, 1965 FIG. 8 is a developed View of the impact-causing cam surface of FIG. 3;

FIG. 9 is a developed cam surface of another type of impact-causing cam; while FIG. l() is an enlarged central sectional view of an impact selector adapted to replace that of FIG. 5 in the tool of FIGS. l, 2 and 3.

I have chosen to describe an embodiment of my invention as shown in FIGS. l, Z and 3 wherein a housing 10 encases the parts of this invention, the drive means is an electric motor housing in the portion 11 shown in the drawing and provided with ya hand grip 12 and a trigger 13 for actuating the electric motor in the usual manner.

A housing portion 14 provides a gear reduction between the driving motor 11 and the driven shaft `of the tool in the housing portion 1G as will be later described. A chuckAlS is connected to be driven by the improved tool of this invention but the chuck itself forms no part of the present .inventionV but is disclosed and claimed in my copending application Serial No. 143,695, filed OC- tober 9, 1961, now Patent No. 3,132,871.

Referring now to FIG. 3, within the housing 10 is a shaft 16 having a drive end 16a and a tool attached end leb. The drive end 16a is non-circular and in the present instance is provided with two opposite parallel llat faces adapted to be received telescopically in a 4female socket 17 which has threaded attachment at 18 to the output shaft 19 of a gear reduction 20 which `in turn is driven by a shaft 21 connected to an electric motor (not shown) within the housing portion 11. It will be noted that there is a space 22 between the shaft end 16a and the shaft 19 to provide an end play which prevents ltransmission of impact blows from the tool back to the hand held motor.

The tool attached end 16b of the shaft 16 has a driving connection 23 within an anvil 24 which terminates in a threaded connection 25 by which chuck 15 is attached to the drive shaft. This chuck is adapted to hold a tool in acollet 27.

The anvil 24 is provided with a bearing Within the housing 11i at the left-hand end of FIG. 3 by means of a roller bearing 23 having a plurality of rollers .28a held for rotation on axes parallel to the axis of shaft 16. The outer race of this roller bearing fits snugly in the housing 1i) and the inner race is preferably provided by a cylindrical surface on the anvil 24. This provides a line contact between the rollers 28a and the surface of the anvil 24 which permits a slight axial lmovement of the anvil during impact ,operation of the tool aswill be presently described. At the same time, the elongated roller bearings give a good alignment between the shaft 16 and the anvil 24 `inside of the housing 1t). The shaft 16 is provided with bearings at the right-hand end by means of a ball bearing 29 whose inner race engages the shaft 16 and whose vouter race is firmly held in a thrust sleeve 30 which has threaded engagement with the housing 1t). The outer race of this bearing is firmly held between a shoulder 30a on the sleeve 3lland a retainer ring 31 which snaps into apsuitable groove in the sleeve 30. The inner race of the bearing 29 is firmly held on the shaft 16 by means of a retainer ring 32 on one side and another retainerring 33 on the other side, both of which snap into suitable receiving grooves in the shaft 16 as will later appear. The flush sleeve 3d 4isfheld in adjusted position by means of a lock ring 34 having a threaded engagement with the housinglil. I find thatan ordinary lock ring will not-hold -in this position in a tool subjectY torepeated impacts such 'as the one described and,therefore, I provide a novel holding arrangement best seen in FIGS., 3 and 6 wherein the ring 34 engagesn against two ball bearings 35 which are located to one side of theaxis of shaft 16 in suitable recesses in the end of sleeve 30 and are weight for delivering the blow to the anvil.

engaged by the lock ring when tightened by a tool engaging the notches 36 so as to cause a slight cocking of the ring 34 due to the bearings 35-holding one -side of the ring out of line with thev opposite side thereof. This gives Ysufficient binding of the threads at 16d so that the adjustment'is'held accuratelyr even in a vibrating tool.

The connection at 23 between fthe anvil 24 and the shaft 16 is by means of one or more ball bearings 37 each of which engages in a recess 38`in the shaft end 16b,-'this recess being approximately 11/2 `times the diameter of the ball 37 as to length, just wide enough to hold the ball 37 rotatably, and shallower in depth than `the diameter of yball* 37 so that the ball is held in a suitable opening in theuanvil 24 by means of aset screw 39l which has a Y recessedradially inner end engaging the surface of ball vlseen in FIG. 3, the hammer completely surrounds the shaft 16 and its shape is such that the amount of metal may be varied in different `size hammers so as to satisfy the different working conditions requiring a different Novel means is provided for securing the hammer to the shaft for rotation therewith but for reciprocation relatively thereto longitudinally. The preferred form shown herewith comprises a plurality of elongated grooves 41 in said hammer i (three being indicated in FIG. 7) opening toward the shaft 16 and parallel to the axis of the shaft.

These grooves are evenly spaced arcuately 120 degrees apart about the shaft. A plurality of ball receiving recesses 42 are provided -in the shaft 16, at least two to each groove *l as shown in FIG. 3, these shaft recesses being aligned semi-spherical and the cross section of each groove 41 is substantially that of a half circle so that the diameters of the recesses and grooves snugly receive each ofthe balls 43. Y It results from this construction that the hammer is keyed to the shaft 16 so as to rotate therewith and has substantially frictionless reciprocation relative to Y the shaft.

Cam and follower means is provided to cause repeated reciprocation of the hammer 40 and release thereof to hit the anvil 24 while the shaft 16 continues to rotate. In this embodiment, a cam 44 is formed integrally with the hammer 40 and this cam has at least one, and preferably a plurality, of inclined portions 44a extending longitudinally toward the tool attached end and in a direction opposite to the shaft and cam rotation. This inclined portion terminates in a sharp shoulder portion 44h dropping 'away toward the drive end of the shaft, and then a notch portion 44C joining withvan adjacent inclined portion 44a. The cam 44 is shown developed in FIG. 8 so that these parts may be clearly seen. In the form shown in the present embodiment, four such cam incline portions and sharp shoulders are utilized but quite often when using larger drills the cam 44as shown in FIG. 9 might be of greater arcuate extent (or of the same arcuate extent) and would be supplied with similarly numbered inclined portions, shoulders and notches as indicated in side of hammer 40 and cam 44 toward the operator and this spring is held between the shoulder 44a on cam 44 and a spring retainer 26 which embraces shaft 16 and is slidable therealong. The spring 45 is loaded as the cam 44 moves toward the right in FIG. 3 as a cam follower 46 rides up the inclined portion 44a and then the spring 45 delivers a ysharp blow of the hammer 40 against the anvil 24 as the force of the spring is released when the follower drops off one ofthe sharp shoulders 44b. It will be noticed that the spring retainer 26 engages against retainer ring 33 which in turn engages in ,one of the grooves 33a in shaft 16; A plurality of these grooves 33a is provided, three being shown, ,so that the position 'of bearing 29 and the position of the spring retainer 26 may be changed to one of several locations. Referring to FIG. 3, it will be noted that the retainer ring 33 is in the middle of three notches 33a while the retainer ning 32'is in the middle of three notches 33b. It is obvious that both of these retainer rings may be moved either to the left or the right as shown in FIG. 3 either to change the compression on the spring'45 or to accommodate a 4[spring in place of 45 which iseither shorter or longer than the spring shown in the drawing.

The follower 46 is rotatably mounted in a fitting 47 which is threaded into the housing 1f).- As shown in FIG. 3, the follower has a portion of enlarged diameter at 46a which is slidable in a'cylindrical chamber 48 which is preferably packed with grease.` Acontrol knob 49'has Aa threaded connection with the fitting 47 and when this knob is screwed on the threads toward the tool, it presses through a thrust bearing 50 against a shoulder 46h on the follower soas to carry it inwardly. When l'the control knob 49 is threaded'on the fitting 47 to carry it away from the tool, a retainer ring 51 seated in a suitable notch in the end of the follower 46 serves to carry the follower radially outwardly. A cap 52 is pushed into a suitable opening Iin the control knob 'so as to close off the parts in la suitable manner. A spring lock 53 is held in Ycompression between the control knob 49 and the fitting 47 Whenthe follower isin its radially innermostposition as shown in FIG. 3 and this locks the follower against displacement when-'the tool isin its impact operation. The cam follower 46 can be moved radially outward from the position in full lines in figure to the dot-dash position so as to clear the cam 44. In this position, a springlock-washer v54 is compressed between follower portion 46a and the fitting 47 so as to prevent accidental dislodgement of the follower. Y Y

An alternative form of impact controller is shown in FIG. l0. Here the follower 46 is rotatably mounted in a fitting 47 threaded into the housing 10. A control `being held in place by a screw 56. This permits the follower '46 .to 'rotate while it is performing its function butat the same timefpermits theknob v49 to `carry the follower 46 radially inwardly and outwardly asthe knob 4Vis threaded on the fitting 47.- A helical compression spring. 57 held between the control knob and a retainer ring 58 puts a tension on the threaded connection between knob 49 and fitting 47' so that the parts willhold their adjusted position. An O-ring seal is provided at 59.

A shaft lock is provided to holdtheshaft 16 from turn- `ing while the chuck 15 is being threaded on or off the Ithreads 25.l This comprisesxan opening 60 radially extending into an anvil 24 and enterable by a pin 61 which is normally held in its radial outward position by a compressionspning 62 held between a retainer ring 63 engaged in the threaded fitting 64 which is threaded into the housing 10, and another retainer ring'65 which engages in annular notch in the pin 61. Normally, the hole 60 is out of alignment with thepin 61: and it is necessary to first push the chuck 15 backwardly against spring 45 until the operator can push the pin 61 into the hole 60. Then release of pressure on the chuck 15 will permit the spring 45 to retain the pin 61 frictionally in the hole 60 while one rotates the chuck 15 relative to the anvil 24.

A seal 65 is provided at the left-hand end of housing 10 against anvil 24 to prevent entrance of dirt there or escape of lubricant from the tool. A small vent hole 67 is provided through anvil 24 to vent the air space between the lefthand end of shaft 16 and the receiving recess in the anvil.

Further description of the chuck l is believed unnecessary because it has no part in the present invention and is fully disclosed in the copending application mentioned above. However, it is suicient to state that the collet 27 is provided with evenly spaced radially extending steel plates between which rubber is molded and when the cap 68 is threaded on the threads 69, the mating inclined surface at '70 cause the collet to squeeze radially inwardly or outwardly against a tool bit passing through the center of the collet.

The operation of my device should now be obvious. All of the working parts except the impact selector and the drive means may be assembled externally of the housing It) so that one can be certain that all of the parts are properly assembled before placing them inside of the housing. These parts which may be so assembled are the shaft 16, the anvil 24, the bearing 23 between the anvil and the housing 1u, the hammer 4t) and cam 44, the impact-causing spring 45, the spring retainer 26, the bearing 29, the thrust sleeve 3i) and the retainer rings 31, 32 and 33. This complete assembly is then entered through the right-hand open end of housing as shown in FIG. 3 and the thrust sleeve 3G is threaded into the receiving threads in housing 16. At this time, an adjustment is made by taking the assembled cam follower 46, running it into its radially innermost position and then adjusting the threads between thrust sleeve 3u and housing it) so that the follower 46 just clears the notches 44C in the position of the parts of FIG. 3, namely, when the hammer 4t) is striking the anvil 24. At this point, if the cam notch 44e struck the follower 46 before the hammer 4l) struck the anvil 24, then the force of the blow would be lost and dissipated. However, one wants to come as close to the position as possible so as to get the full force of the action of the spring urging the hammer 4t) against the anvil. This can be adjusted very nicely by moving the thrust sleeve along its associated threads in housing 10 which pushes all of the parts assembled on the shaft longitudinally by a small amount to achieve the desired relationship. The lock ring 34 is then screwed into position so as to hold the adjustment already set. It is obvious that the housings 10 and 14 may be brought together longitudinally while entering the non-circular shaft end 16a into its coordinate receiving socket 17 by a telescoping action. The housing 14 is held to the housing l@ positioned by an extending collar 14a and a dowel pin 14h and held in position by two screws '71 which are diametrically opposite each other and which pass through the partition 14C and into the metal of the housing 1G.

It will be obvious that the housing 1I is held to the housing 14 by means of a plurality of screws 72. The assembly of the chuck 15 on the threads 25 of the anvil 24 has already been explained.

With the motor inside thehousing 11 in operation, the drive means will rotate the shaft I6. With the follower 46 in its radially outermost position, all of the parts will rotate Vin the FIG. 3 position and the tool held by the collet 27 will rotate in the usual manner of a drill. If impact is desired, then the follower 46 is moved to its radially innermost position as shown in FIG. 3 whereupon the rotation of shaft I6 will carry the cam 44 in a circular path, the inclined portions 44a of the cam will ride on the follower 46 moving the cam from the position of FIG. 3 to the position of FIG. 4 and then, as the shoulder 44h of the cam passes the follower 46, the spring 45 will urge the cam and the hammer 40 toward the left as viewed` in FIGS. 3 and 4 so as to deliver a sharp blow between the hammer 40 and the anvil 24. This action is repeated as often as the shoulders 4411 o the cam pass the follower 46.

It is important that the parts be properly designed to obtain the most efficient operation with the power available. One form of my tool, capable of very wide use, utilizes a half horse power motor turning at 1200 revolu- Vtions per minute and impact being provided by a hammer 4t) weighing between 3/s and 1/2 pound with the cam 44 having four lobes or inclined projections 44a, each adapted to lift the hammer 1A inch. With the hammer weighing /s pound, I utilized a spring which in the assembled position of FIG. 3 exerted a force of 20 pounds and when compressed 1A inch by the action of the cam lobes exerted a force of 28 pounds. With a hammer weighing 1/z'pound I utilized a spring which in the assembled condition exerted a force of 28 pounds and when compressed 1A inch by the action of the cam exerted a force of 53 pounds. The force of the impact exerted by the hammer is calculated according to the well known formula mv?. The more important factor in this formula is, of course, the velocity and I have therefore determined that increasing the weight or mass of the hammer 4u was not as important as having an increased velocity at the moment of impact due to the urgino of the spring. The heavier the hammer, the more dimcult it is for the spring to start the hammer in the blow delivering direction after release by the cam. It is important to coordinate the speed of the motor, the number of lobes on the cam 44, and the character of the spring 45 so that the hammer itl when released from one of the shoulders 4411 has time to substantially reach the recess 44e so as to deliver the full capability of the tool. In a tool adapted for wide general use, as above described, I have determined through extensive experiments with many diiferent ceramic materials and with many variations of power distribution between the rotary and percussive forces involved, that the most effective tool -is provided when the total net power transmitted to the drill bit from the motor for utilization in doing the work of removing ceramic materials of the type described in this application is in the proportion of one part for percussion production and two to three parts for rotation production. In general, the proportion applied to rotation is selected within the limits given dependent upon the general range of the material to be drilled. I have obtained the best results when dividing the net power in the ratio of one for percussion to two for rotation when drilling harder materials and in the ratio of one for percussion to three for rotation when drilling softer materials.

What is claimed is:

1. In ya rotary impact tool comprising a housing open at its front and rear ends, a constantly rotatable shaft adapted to be journaled in said housing, said shaft having a drive end and an anvil attached end, drive means rigid relative to said housing and drivingly connected to said drive end by a longitudinally disconnectable coupling, an anvil annularly surrounding said anvil Iattached end of said shaft and secured thereto to rotate therewith, a

Alow friction bearing annularly surrounding said anvil and engaging between said anvil and said housing, said anvil ladapted to carry a tool chuck, a hammer annularly surrounding said shaft on the side of said anvil toward said drivenend of said shaft,means securing said hammer to said shaft for rotation therewith and for longitudinal movement relative thereto, a thrust sleeve surrounding said shaft near said drive end thereof, said sleeve having a threaded engagement with said housing, a combined radial and thrust bearing engaged between said shaft and said sleeve and iixed against longitudinal movement relative to said shaft `and sleeve, a spring retainer surrounding said shaft and having rigid engagement with said last named bearing, a helical compression spring embracing said shaft and engaged between '3,1 viese said hammer and said spring retainer, a cam member rigid with said hammer and extending arcuately about said shaft axis, said cam member having at least one incline portion extending longitudinally toward said anvil attached end in a direction opposite to shaft and cam rotation, said incline portion terminating in a sharp shoulder portion dropping away toward said drive end and then a notch portion joining `with an adjacent incline portion, a cam follower member carried by said housing and movable radially between .cam member engaging and disengaging positions for respectively causing or omitting reciprocating blows of said hammer against said anvil as said shaft rotates, whereby one may assemble said shaft, anvil, bearing between anvil .and housing, hammer and cam, spring, retainer, thrust sleeve and bearing between sleeve and shaft as a single unit which may then be inserted endwise in said housing to engage said driving coupling at said drive end.

2. A tool as defined in claim 1 wherein said longitudinally disconnectable coupling comprises non-circular' vmutually telescoping male and female members, one on said shaft and the other on said drive means, there being f lost motion between said last named members permitting shifting of said shaft relative to said drive means by move, lment of said thrust sleeve along its associated threads,

and wherebyimpact action on a tool carried by said anvil is not transmitted back to said drive means.

3. A tool as defined in claim 1 wherein said anvil is Y attached to said shaft by means of a ball bearing held in a suitable'opening in said anvil adjacent said shaft, there being a recess in said shaft at that point havlng an arcuate width approximately the diameter of said ball bearing and having `a depth less than the diameter of said ball bearing so that said ball bearing lies partly in said recess and partly in said'anvil acting as a key, and said recess having a longitudinal extent greater than the diameter of said ball bearing, whereby impact action by reciprocation of said hammer when said tool is applied against work is ktransmitted to said anvil onlyl and not through said shaft to saidhousing,rthus reducing inertia load upon said drive means. 4. A tool as defined in claim 1 wherein said bearing between said anvil and said housing is a roller bearing having rollers on axes parallel to the axis of said shaft and anvil, and said -anvil has a cylindrical outer surface providing in the inner race of said bearing, whereby an elongated contact is provided betweensaid rollers and said anvil, and said roller bearing provides good alignment of s-aid anvil and shaft relative to said housing.

5. A tool as defined in claim 1 wherein said means securing said hammer to said shaft comprises a plurality of elongated grooves in said hammer opening toward said shaft and parallel to the axis of said shaft, said grooves being evenly spaced arcuately about said shaft, a plurality of ball-receiving recesses in said shaft, at least two for each groove, said shaft recesses aligned respectively with said grooves, `and a ball in each of said shaft recesses, the

depth of said recesses and grooves being such that each ball isV snugly held partly in its recessand partly in its associated groove, whereby said hammer is keyed to ,saidY shaft and has substantially frictionless reciprocation relative thereto.

6. A tool as defined in claim 1 wherein, between said spring retainer and said combined radial and thrust bear- ,f 8 easily adjusted or vdifferent size springs may be mounted between said hammer and saidspring retainer.

7. A tool as deiined in claim l including a locking nut adjacent said thrust sleeve and having threaded engagement with said housing, and at least one eccentric projection between said sleeve rand said nut, whereby to cause cocking of said nut when the same is pulled into tight engagement against said sleeve to cause binding of said nut-holding threads so that said nut is not loosened by impact drilling. Y

8. A tool as defined in claim 1 including an impact Ycontrol assembly including a fitting secured to said housingopposite said cam member, said cam follower member lbeing rotatably mounted in said fitting and reciprocatable v cam follower member is in either of its two positions and holding said control knob against loosening of its threaded engagement with said fitting.

10. In a rotary impact tool comprising a housing, a

constantly rotatable shaft journaled in said housing, said shaft having a drive end and an anvil attached end, an electric motor rigid relative to said housing and drivingly connected to said drive end, an anvil attached to said shaft and operatively associated with said tool to transmit axial `impact thereto, `a hammer annularly surrounding said shaft on the side of said anvil toward said driven end of sai-d shaft, means securing said hammer to said shaft for rotation therewith and for movement axially relative thereto, a helical compression spring embracing said shaft and engaged between said hammer and an element fixed relative to said housing, a cam member rigid with said hammer and extending arcuately about said shaft axis, said cam member having at least one inclined throw portion extending longitudinally toward said anvil attached end in la direction opposite to shaft and cam rotation, said inclined portion terminating in a sharp lshoulderrportion dropping away toward said drive end and then a notch portion joining with an adjacent inclined portion, a cam follower member carried by said housing and movable radially between cam member engaging 'and disengaging positions forrespectively causing or omitting reciprocating blows of said hammer against said anvil as said shaft rotates; the combination therewith of a hammer weight,

- cam throw portion axial extent, spring strength, and shaft rotational speed such that the total net power applied to the tool is in the proportion of one part for causing impact to between two and three parts for causing shaft and tool rotation.

References Cited in the fileof this patent UNITED STATES PATENTS 2,223,727 nomen Dec. 3,A 1940 2,293,443 Mossberg Aug. 18, 1942 2,457,565 Kott Dec. 28, 1948 3,006,202 Moorhead Oct. 3l, 1961 3,090,450 Fulop May 21, 1963 3,107,083 PeWtherS Oct. 15, 1963 FOREIGN PATENTS 884,064 Great Britain Dec. 6, 1961 

1. IN A ROTARY IMPACT TOOL COMPRISING A HOUSING OPEN AT ITS FRONT AND REAR ENDS, A CONSTANTLY ROTATABLE SHAFT ADAPTED TO BE JOURNALED IN SAID HOUSING, SAID SHAFT HAVING A DRIVE END AND AN ANVIL ATTACHED END, DRIVE MEANS RIGID RELATIVE TO SAID HOUSING AND DRIVINGLY CONNECTED TO SAID DRIVE END BY A LONGITUDINALLY DISCONNECTABLE COUPLING, AN ANVIL ANNULARLY SURROUNDING SAID ANVIL ATTACHED END OF SAID SHAFT AND SECURED THERETO TO ROTATE THEREWITH, A LOW FRICTION BEARING ANNULARLY SURROUNDING SAID ANVIL AND ENGAGING BETWEEN SAID ANVIL AND SAID HOUSING, SAID ANVIL ADAPTED TO CARRY A TOOL CHUCK, A HAMMER ANNULARLY SURROUNDING SAID SHAFT ON THE SIDE OF SAID ANVIL TOWARD SAID DRIVEN END OF SAID SHAFT, MEANS SECURING SAID HAMMER TO SAID SHAFT FOR ROTATION THEREWITH AND FOR LONGITUDINAL MOVEMENT RELATIVE THERETO, A THRUST SLEEVE SURROUNDING SAID SHAFT NEAR SAID DRIVE END THEREOF, SAID SLEEVE HAVING A THREADED ENGAGEMENT WITH SAID HOUSING, A COMBINED RADIAL AND THRUST BEARING ENGAGED BETWEEN SAID SHAFT AND SAID SLEEVE AND FIXED AGAINST LONGITUDINAL MOVEMENT RELATIVE TO SAID SHAFT AND SLEEVE, A SPRING RETAINER SURROUNDING SAID SHAFT AND HAVING RIGID ENGAGEMENT WITH SAID LAST NAMED BEARING, A HELICAL COMPRESSION SPRING EMBRACING SAID SHAFT AND ENGAGED BETWEEN SAID HAMMER AND SAID SPRING RETAINER, A CAM MEMBER RIGID WITH SAID HAMMER AND EXTENDING ARCUATELY ABOUT SAID SHAFT AXIS, SAID CAM MEMBER HAVING AT LEAST ONE INCLINED PORTION EXTENDING LONGITUDINALLY TOWARD SAID ANVIL ATTACHED IN A DIRECTION OPPOSITE TO SHAFT AND CAM ROTATION, SAID INCLINE PORTION TERMINATING IN A SHARP SHOUDLER PORTION DROPPING AWAY TOWARD SAID DRIVE END AND THEN A NOTCH PORTION JOINING WITH AN ADJACENT INCLINE PORTION, A CAM FOLLOWER MEMBER CARRIED BY SAID HOUSING AND MOVABLE RADIALLY BETWEEN CAM MEMBER ENGAGING AND DISENGAGING POSITION TERSPECTIVELY CAUSING OR OMITTING RECIPROCATING BLOWS OF SAID HAMMER AGAINST SAID ANVIL AS SAID SHAFT ROTATES, WHEREBY ONE MAY ASSEMBLE SAID SHAFT, ANVIL, BEARING BETWEEN ANVIL AND HOUSING, HAMMER AND CAM, SPRING, RETAINER, THRUST SLEEVE AND BEARING BETWEEN SLEEVE AND SHAFT AS A SINGLE UNIT WHICH MAY THEN BE INSERTED ENDWISE IN SAID HOUSING TO ENGAGE AND DRIVING COUPLING AT SAID DRIVE END. 